I never changed the plugs in the 2 points with MSD 6 cars I owned, I put at least 30,000 miles on one set-still going when I sold it, I feel the MSD is the best thing ever invented for points and street performance engines, this was back in the leaded gas era and I can assure you an L-78 would not go 15,000 miles on a set of plugs in daily driving on standard Delco ignition system